Far Sync instances are a feature of Oracle Data Guard designed to support zero data loss protection over long distances:
The Data Guard Broker must be used to deploy and manage Far Sync instances (A): Data Guard Broker simplifies the deployment and management of Far Sync instances, which are an integral part of zero data loss protection configurations.
They enable standby databases to be configured at remote distances from the primary without impacting performance on the primary (C): Far Sync instances are designed to receive redo from the primary database and then forward it to a remote standby database, thereby avoiding any performance impact on the primary database itself.
A primary database can ship redo directly to multiple Far Sync instances (E): A primary database can be configured to send redo logs to more than one Far Sync instance, which can then forward the redo to their respective remote standby databases.
Reference:
Oracle Data Guard Concepts and Administration Guide
Oracle Database High Availability Overview